The present invention relates to hydrophically modified urethane polymers, which are used as rheology modifiers in waterborne coatings formulations.
Rheology modifiers are used in waterborne coatings formulations to control viscosity over a wide shear rate range. They may be associative (they associate with the dispersed phase) or non-associative (they thicken the water phase). Associative thickeners may be derived from natural products such as hydrophobically modified cellulose ethers, or prepared from synthetic polymers such as hydrophobically modified ethylene oxide urethane (HEUR) polymers. A typical description of HEUR polymers and their preparation can be found in US 2009/0318595 A1, which describes forming a combination of linear and branched HEUR polymers by reacting a polyglycol, a hydrophobic alcohol, a diisocyanate, and a triisocyanate together in a one-pot reaction.
U.S. Pat. No. 4,155,892 (Emmons et al.) describes the preparation of linear as well as branched HEUR polymers in separate examples.
Rheology modifiers are typically classified as either low shear rate viscosity builders (Stormer viscosity builders, also known as KU viscosity builders) or high shear rate viscosity builders (ICI builders). It is desirable to increase ICI viscosity and the efficiency of ICI building rheology modifiers without concomitant increase in KU viscosity because such increase limits the formulator's ability to add a KU building rheology modifier to the formulation.
The commercially available HEUR polymers ACRYSOL™ 5000 and ACRYSOL™ 6000 rheology modifiers (a trademark of The Dow Chemical Company or its Affiliates) exhibit ICI viscosities of 1.75 and 2.40 respectively and KU viscosities of 79.3 and 109.7 respectively in an acrylic semi-gloss white paint. It would be advantageous to obtain a hydrophobically modified urethane polymer formulation with an increased ICI/KU viscosity ratio in comparison to these known rheology modifiers.